I want to compute something like :
`Conjugate[
 Sin[\[Theta]] (I (2 Sqrt[2] f + h[x]) + 
     Sin[\[Theta]] \[Eta][x]) Derivative[1][h][
    x] + ((1 + I) Sqrt[2] f (1 + I Cos[2 \[Theta]]) + 
     h[x] Sin[\[Theta]]^2 - (Cos[\[Theta]]^3 + 
        I Sin[\[Theta]]^3) \[Eta][x]) Derivative[1][\[Eta]][x]] // Refine`

I have a list of assumptions requiring that all the quantities (also the derivatives) are reals so, in principle, Mathematica should be able to replace the I by -I, problem is it does not...

Why is it so difficult for Mathematica to replace the I by -I, I really don't understand because it seems so simple...

Does anyone have a clue why it doesn't work ?

(I also tried Simplify / FullSimplify instead of Refine and it doesn't work as well)

Thank you in advance ;)